1. Field of the Invention
The present invention relates to an insulation-coated electric conductor.
2. Description of the Related Art
A conductor coated with an electrical insulating material is incorporated in a variety of electric machinery and tools and used in large quantity for uses for coils. It is especially abundantly used in electric machinery and tools as represented by motors and generators. A winding, having a conductor whose cross-section has a non-round shape, and being spirally covered with, as a coating material, an insulating material, such as glass and paper, has conventionally been used. Such a winding has been used for parts of machinery and tools required to have extremely high reliability, such as for coils for generators of power plants, coils for transformers, coils for vehicular driving motors, and the like.
Recently, a winding having a conductor whose cross-section has a non-round shape, such as an approximately rectangular shape, tends to be used also in machinery and tools smaller than the machinery and tools described above. Even in these small machinery and tools, they are required to be made high performance in a shape of coil. Accordingly, a method for forming a coil by joining coated conductors together each having a cross-section shape corresponding to the coil shape, tends to be employed as the coil production method, in stead of the conventional method for producing a coil by winding an electric wire circumferentially with a coil, a so-called wire-winding. Employment of such a winding of a conductor with a shape other than round in a small machinery and tools is developed, because a gap between the winding and a core of the coil can be eliminated and magnetic field loss can be lessened, to resultantly improve performance of the coil, and also because the coil to be used in a small machinery and tools can further be miniaturized. Making the conductor have a shape other than round makes it difficult to wind a long electric wire, as it is, directly onto a core of a coil, when forming a coil-like circuit. Therefore, a technique which has recently been employed involves steps of, at first, forming short conductors into partial shapes of a coil, and then forming an entire circuit by welding the conductors to join together.
To form such a coil, the conductors are required to be connected to one another. To connect the conductors, the parts where soldering has conventionally been conducted are to be subjected to an electric welding method, such as fusing (electric welding while applying pressure), TIG welding, and the like. This is because, it is recently required to use a material having the same level of performance as a conductor (such as copper) currently used, as a connection material, since with a conventionally employed soldering, a serious environmental effect is caused by lead or the like contained in the solder, when used products are discarded, and also the soldered parts are inferior in reliability to vibration of machinery and tools.
Conventionally, as coating materials to be used for round enameled wires, a variety of resins, such as polyesters, have been used. However, since the conductors are to be connected to one another by directly heating the conductors and melting them in fusing and TIG welding, the insulation coating on the periphery of the connected portion is heated to an extremely high temperature, to receive considerable thermal deterioration. For example, to connect copper pieces to each other by usual welding, the temperature of the copper pieces must be increased to the melting point of copper or higher, and for that, the conductor temperature is increased to about 1,100° C. or higher. The increase of the conductor temperature causes thermal deterioration of the insulation coating on the periphery of the connected portion of the conductors, and further, low-molecular-weight components in the coating material are evaporated by the heat, to result in blistering (foaming) in the coating. As a result, the electric properties of the coating material on the periphery of the connected portion are possibly deteriorated in some cases. That such welding heat affects the coating has been well known, and to lessen the effect is necessary also, to improve the reliability of electric machinery and tools. If the conductor temperature reaches 1,100° C. in a welded portion, the heat that a coating, required to have insulating properties, receives reaches as high as about 600° C. at 10 mm distance from the welded portion. Further, the above-described blistering of the coating cannot be avoided if polyamideimide resin, which has conventionally been used, is used solely.